ISBNs and barcodes

ISBN stands for International Standard Book Number.
The barcode is a visualisation of the ISBN.
I am often asked, do I need an ISBN and barcode?
If the book is being distributed for sale in any way, it must have an ISBN and barcode featured on the book.
If the book is only being given away, it does not require an ISBN or barcode.
Every new book needs its own unique ISBN.
This includes revisions of an already published and then re-released book or a paperback version of a hard-cover book.
The ISBN must first be purchased, then you can also buy the barcode visualisation of it.
An e-book does not need a barcode but still should have an ISBN assigned to it for identification purposes.
What is an ISSN?
An ISSN is a small barcode that you may see next to the main ISBN.
It is usually included in serial publications such as magazines or journals under a single title.